Tennant will portray the title character for a Christmas episode and four additional hour-long episodes in 2009 and early 2010. However, the actor said that when the series returns for a full season in 2010, "it won't be with me."
"This show has been so special to me," Tennant said. "I don't want to outstay my welcome."
It isn't clear who will replace Tennant as of yet, or if a search to re-cast this doctor who can regenerate into a new body has begun.